Pharmacokinetic Phase of drug action describes the time course and deposition of a drug in the body, based on its absorption, metabolism, and elimination

Definition of Absorption

1)The process by which a drug gets introduced to the body in a way it can be distributed
2)Involves the ability (or inability) of a drug to cross different barriers (cell membranes, lipid membranes, etc).

Distribution

1)Process by which a drug is transported to its sites of action, eliminated, and stored

Distribution Continued

1)Intended distribution may be systemic or local
2)To be effective, a drug must deliver a high enough concentration at an intended site

Metabolism of a drug

Complex Processes that cause the biotransformation or metabolism of a drug

Where is the main site of drug metabolism

In the liver

Elimination phase

1)Primary site for the excretion of drugs is the kidneys
2)Maintenance dose-dose needed to equal the rate of elimination to maintain a steady concentration of the drug

Critical threshold

The minimum of drug concentration needed for a therapeutic effect

L/T ratio

Lung availability versus total systemic availability

Factors increasing the L/T ratio with inhaled drugs

1)Efficient delivery devices
2)Inhaled drugs with a high first pass metabolism
3)Use of a resovoir device

Pharmacodynamic phase

Describes the mechanisms of drug action by which a drug molecule causes its effects on the body

Structure/Activity relations in the pharmacodynamic phase

Relationship between a drug's chemical structure and its clinical effect or activity

Nature and type of drug receptors

1)Most receptors are proteins or polypeptides whose shape and electric charge provide a match to the drug's corresponding shape and charge.
2)Receptor proteins can be found on the cell's surface and within the cell
3)Resultant complex molecular mechanism translates, or, even better, tranduces a signal into an intracellular sequence that controls cell function

Types of transmembrane signalling

1)Lipid soluble drugs cross the cell membranes and act on intracellular receptors
2)Drug attaches to an extracellular portion of a protein receptor which projects into the cell's protoplasm
3)Ion channels
4)Second messenger system

G protein signalling

Drug attaches to a transmembrane receptor that is coupled to an intracellular enzyme by a g protein